U.S. Pat. No. 3,540,047 to Walser et al discloses thin film magnetodielectric materials that have proven quite effective in electrical devices of the type referred to above.
According to the patent, the materials comprise a substrate and a plurality of discrete thin film elements arranged in orderly array on the substrate. Each element is comprised of a thin film layer of magnetic material or a plurality of thin film layers of magnetic material separated by intervening, alternating, thin film dielectric insulating layers. In the preferred embodiment illustrated, the elements are rectangular in shape and arranged on the substrate in a uniform pattern of rows and columns.
The uniform, grid like array of the elements is obtained by covering the substrate with a deposition mask during deposition of the metal and dielectric layers, or by post deposition photo-resist acid etching; primarily costly and complex pattern etching.
The magnetic material is preferably a nickel-iron or nickel-iron-cobalt alloy commercially available under the tradename "Permalloy"; the insulating layers are preferably silicon oxide, but could also be magnesium fluoride or zinc sulfide; and the substrate may be glass, foil or polymer film. The materials are described as having significant advantages over materials having a continuous thin film of metal. However, the materials of Walser et al are available only in sheet form and have a very low effective volume fraction of magnetic material, i.e., the ratio of the volume of magnetic material to the total volume of the substrate, the dielectric insulating layers and the magnetic metallic layers.